Method and apparatus for assessing the effect of yarn faults on woven or knitted fabrics

ABSTRACT

The assessment of the effects of yarn faults is carried out by simulating the fabric image. In a first step, the yarn is examined by a measuring member for parameters associated with the volume and/or the surface. In a second step, these parameters are converted into grey values or color values, and these values are assigned to image spots. Finally, the image spots are reproduced on a video display unit and/or a printer. An image is generated thereby, representing a simulation of a woven or knitted fabric produced from the examined yarn.

This application is a continuation, of application Ser. No. 08/531,485,filed Sep. 21, 1995, which was a Continuation-in-part of applicationSer. No. 08/077,682 filed Jun. 16, 1993, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for assessingthe effect of yarn faults on woven or knitted fabrics produced from therespective yarn by simulation of the fabric image.

BACKGROUND

Traditional methods of this type use so-called display boards forsimulating the fabric image. The respective yarn is wound spirallyaround trapezoidal or rectangular pieces of cardboard or metal sheets,thereby forming a kind of quasi woven or knitted fabric, from whichpossible fault patterns can be seen clearly. The display boards aretherefore a valuable aid in estimating whether and to what extent aparticular yarn is suitable for a particular fabric, and they allowpredictions to be made on one of the most important quality features ofthe finished product, namely its appearance.

However, the production of the display boards by the winding of yarnaround metal sheets is relatively labor intensive and is also no longerin keeping with the times, so that there is a need for a new method forsimulating the fabric image. This new method should necessitate aslittle outlay as possible in terms of labor, it should be flexible andit should give reliable and reproducible results.

SUMMARY OF THE INVENTION

According to the invention, the following steps are carried out toassess the effects of yarn faults on the appearance of fabricscontaining such yarns:

a. examination of the yarn for parameters associated with the volumeand/or the diameter and/or the surface;

b. conversion of said parameters into grey values or color values andassignment of these values to image spots; and

c. reproduction of the image spots to produce an image which representsa simulation of a woven or knitted fabric produced from the examinedyarn.

An apparatus according to the invention is characterized by a measuringmember for determining parameters associated with the volume and/or thesurface of the yarn, by a computer for converting said parameters intogrey or color values, by means for assigning the grey or color values toimage spots, by a video display unit and/or a printer, and by controlmeans for reproducing the image spots on the video display unit and/oron the printer for the purpose of simulating a woven or knitted fabricproduced on the examined yarn.

By means of the invention, therefore, the display boards are producedelectronically, and if a uniformity tester, such as, for example, thetesters sold by Zellweger Uster AG under the designation USTER TESTER(USTER being a registered trademark of Zellweger Uster AG), is used as ameasuring device for examining said parameters, the electronic displayboards are calculated from the data conventionally produced. With theUSTER TESTER, which is described by way of example in EP-A-0 249 741 andin CH-A-671 105 (the disclosures of both of which are incorporatedherein by reference), the uniformity and/or the hairiness of a yarnsample among other things are examined and are represented in the formof a graph, a wavelength spectrum or other graphical representations ofthe variations of the measured parameters on a video display unit and/oron a printer. Uniformity and hairiness are two parameters which areessential for the later fabric image and which can be processed at arelatively low outlay in terms of software in order to simulate thedisplay boards.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below by means of an exemplaryembodiment and the drawings in which:

FIG. 1 shows a perspective representation of a test installation fordetermining the mass variations of a textile test material;

FIG. 2 shows a graph of an individual sample obtained by means of thetest installation of FIG. 1;

FIG. 3 shows an excerpt from a composite graphic chart with spectrogramsof two samples; and

FIGS. 4a-4 b show display-board simulations of the two samples of FIG.3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The test installation illustrated in FIG. 1 is the USTER TESTER ofZellweger Uster AG, which is used for determining material and qualitycharacteristics of textile test material, such as, for example, yarns.These characteristics are, for example, mass variations, hairiness orstructure (twist) of the examined yarn. See, in this respect, forexample, CH-A-671 105, EP-A-0 249 741 and U.S. Pat. No. 5,030,841 (thedisclosures of which are each incorporated herein by reference). Faultsin these characteristics have an undesirable effect on the finishedtextile product.

The test installation includes, in known fashion, the actual testappliance 1, an evaluation and operating unit 2 and a printer 3. Thetest appliance 1 is provided with one or more measuring modules 4 whichhave measuring members for the characteristics to be examined. The testmaterial or yarn designated by the reference symbol 5 is transportedthrough the measuring members which continuously measure the mass,hairiness and/or structure and convert them into electrical signals. Thetested yarn 5 is sucked off after the measurement.

The signal and data processing and the functional checking of the testinstallation are carried out in the evaluation and operating unit 2.Variables, measuring conditions and the desired representation of theresults are entered via a keyboard 6, a video display unit 7 and controlkeys 8, and the measuring cycle and results appear in numerical andgraphic form on the video display unit 7. The printer 3 likewise servesfor the output of measured values and of graphic representations andespecially also for the output of complete test reports.

The direct result of the examination of a yarn sample 5 by the testinstallation shown is the exemplary graph which is illustrated in FIG. 2and which indicates the variations of the examined characteristics overthe length of the test material. If, for example, the hairiness is beingexamined, this is defined as the total length of the fibers projectingfrom the yarn body, within a specific length of measuring field (thatis, for example, a specific length of the yarn). The hairiness of a yarnis then the average value of the total lengths of fibers formed over theentire test length.

The FIG. 2 graph shows the variations of the examined characteristicsaround an average value M which corresponds to a standardized value ofthe signal representing the yarn cross-section. The spread or standarddeviation can be calculated from these variations which, for example,are given in percentages when the mass variations are being examined andin absolute values when the hairiness is being measured.

Variations exceeding specific limits are an indication of a fault, andin the faults a distinction is made in a known way between periodic andnon-periodic faults. By definition, periodic faults have a specificwavelength and can be detected in a simple way by means of thewavelength spectrogram, wherein spikes or “chimneys” which occur in thespectrogram indicate a fault. FIG. 3 shows the spectrograms of the massvariations of 2 samples; sample 1 has a chimney with a wavelength of 20m and sample 2 has four chimneys which are in the range below 50 cm.

Depending on the width of the subsequent woven or knitted fabric anddepending on the wavelength of the periodic fault, undesirable patternsoccur in the finished product and often make the finished productuseless. Reference may be made, in this respect, to the publication“Evenness Testing in Yarn Production: Part I” by R. Furter, The TextileInstitute, 1982, in which the influence of periodic mass variations onwoven and knitted fabrics is explained on page 60 ff. These explanationsreveal, among other things, that short-period mass fluctuations with awavelength of 1 to 50 cm lead to a so-called moiré pattern, and thatlong-period mass variations with a wavelength of more than 5 m can causerelatively pronounced cross-stripes in the finished product.Accordingly, a fabric made of yarn of sample 1 (FIG. 3) would havecross-stripes and one made of yarn of sample 2 would have a moirépattern. If hairiness or structure are examined instead of the massvariations, the same relationships basically apply, except that effectsof periodic faults on the finished product are rather great with respectto hairiness and tend to be rather less with respect to structure.

Virtually all periodic faults lead to an uneven appearance in thefinished products, to a so-called “cloudy character”. With respect tonon-periodic faults, the so-called imperfections, neps in particularhave an extremely disturbing effect, because, as a rule, they havedifferent reflection properties from fault-free yarn and, for example,absorb dye differently or not at all. The imperfections are recorded andcounted in the USTER TESTER and are displayed and/or printed outseparately according to types of fault, thick places, thin places andneps.

The signal from the measuring member of the FIG. 1 measuring module 4,which is reproduced in the graph of FIG. 2, and/or the signal processedby the evaluation and operating unit 2, for example the spectrogram ofFIG. 3 and/or the number of neps, are used to generate an image of thewoven or knitted fabric produced from the examined yarn on the videodisplay unit 7. This image then directly shows the attendant the effectsof the yarn faults found by the USTER TESTER on the finished product andthus allows a prognosis of the subsequent fabric image.

The simulation of the fabric image takes place in that the signal, whichrepresent parameters associated with the volume or surface of the yarnare converted into grey values or color values and are assigned to oneor more image spots (pixels), and in that these pixels are subsequentlyreproduced on the video display unit 7 and, if appropriate, also on theprinter 3. In the simulation, the parameters can be displayedalternately or in any combination. For this reproduction, the “yarnguide” is variable. That is, the yarn can be wound spirally, as on aconventional display board, in which case the video display unit wouldreproduce the fabric image on the front side of the display board, orthe display board can, as it were, be optionally made transparent andits front or rear side be superposed on one another. Alternately, theyarn can be guided in only one particular direction, for example fromleft to right, so that the thread is cut off at the right-hand of theboard and is subsequently joined again on the left-hand side.Alternately, the yarn can be superposed crosswise, this corresponding tosimulation of a woven fabric, or a knitted fabric. The image resolutioncan be selected as desired. For example, a plurality of threads lyingnext to one another can be combined, in which case the intensity of theimage spots would correspond to the average value of the threads.Selective evaluations of the data are also possible, for example, byindicating only individual chimneys of the spectrogram or only thedifference from the ideal spectrogram.

Two exemplary categories of signals are basically available as astarting point for calculating the grey values or color values. On theone hand, for a signal generated directly by the measuring member,according to the graph of FIG. 2, and, on the other hand, a signal whichalready represents the results of an evaluation carried out by the USTERTESTER; that is to say, for example, a spectrogram as shown in FIG. 3 orthe results of a nep count. A signal of this second category wouldtherefore represent average values or spreads of selected quantitiesrelevant in textile terms. From the two signal categories, a yarn signalis then simulated for representation on the video display unit. For thesimulation, particular characteristics can be emphasized by measuresknown from image processing, such as contrast accentuation, coloring andthe like.

The following applies in general to the calculation:

I=F(y)

(I: brightness or color step;

y: mass, hairiness, structure, deviation from the average value and soforth)

When calculating from the first category of signals, that is to say froma graph such as that shown in FIG. 2, the following applies:

y=f(x)

(x: position in the longitudinal direction of the yarn), the y-valuesbeing taken directly from the graph.

When calculating from the second category of signals, the followingapplies to periodic faults (spectrogram):$y = {\sum\limits_{i = 1}^{n}\left\lbrack {a_{i} \cdot {\sin \left( {\frac{\pi}{\lambda_{i}} \cdot x} \right)}} \right\rbrack}$

(a: amplitude of the wavelength

i: index of the wavelength in the wavelength spectrogram

λ: wavelength

x: position in the longitudinal direction of the yarn)

The y-values therefore correspond to a reconstructed graph. Any chimneysin the spectrogram are either marked by hand or detected by means of themethod such as that described in Swiss Patent application 2651/91, thedisclosure of which is incorporated herein by reference. As an alternateto calculation by means of the given formula, a fast Fourier transform(FFT) can also be used.

In practice, the following preferably applies to the calculation of I:$y_{1} = {\sum\limits_{i = 1}^{n}\left\lbrack {a_{i} \cdot \left\{ {1 \div {\sin \left( {\frac{\pi}{\lambda_{i}} \cdot x} \right)}} \right\}} \right\rbrack}$

 I=k·{square root over (y₁)} or I=K·y ₁

(y₁: deviation from the minimum value; for this, y is shifted so that y₁is always positive)

(k, K: constant multiplier)

Rare faults occurring at random (that is, imperfections) are taken fromthe corresponding channel of the USTER TESTER and are represented in theimage in terms of their intensity and frequency, the location of therespective image spots being determined by random numbers.

The question as to whether, for the faults occurring relativelyfrequently, one should proceed from the graph to image the real yarn onthe video display unit, or whether one should proceed from thespectrogram and image a simulated yarn reconstructed from statisticalvalues is now answered in favor of the spectrogram. This is becausewavelengths recorded in the spectrogram are usually substantially lowerin number than in the graph since a graph of high resolution wouldproduce a very large quantity of data. There is therefore often no graphavailable which has the resolution necessary for representing thedisplay image.

Moreover, it is questionable whether, for example, neps would berecognized in this image of the real yarn. In contrast, if the neps aretaken from the nep channel and spread in the image in appropriatedensity and with suitable contrast accentuation, such as, for example,coloring, then they are recognized reliably even on the video displayunit. In contrast, the continuous reconstruction of the graph from thespectrogram necessitates a substantially higher computing outlay thanthe direct conversion of the graph into brightness or color values.

FIGS. 4a and 4 b each show a display-board simulation, calculated fromthe spectrograms of FIG. 3, for each of the two samples 1 and 2. Thesesimulations give a result, expected by the average person skilled in theart, with cross-stripes for sample 1 and with a moiré pattern for sample2 which are caused by the periodic faults identified by the hatchedchimneys in the two spectrograms. This result demonstrates thepracticability of the method described.

In accordance with exemplary embodiments of the present invention,simulating the image of a fabric can thus be initiated by simulating ayarn (e.g. on video display screen). However, when simulating a yarn,several problems can arise depending on the specification or quality ofthe equipment used. This is especially true if less expensive and lessperforming equipment (e.g., video displays with reduced resolution) isused.

On a conventional display board wound with yarn, such as that describedin the “Background” portion of the specification, the yarns areseparated by a gap of approximately 1 mm in width. If the board is ofblack color, then the yarns are separated by black rows. When simulatingsuch a display board with a low-cost video display (e.g., computermonitor), the reduced resolution of the monitor compared to the diameterof a yarn may not be sufficient to allocate one pixel or image spot to apoint along a length of a specific yarn and one adjacent black pixel orimage spot to the gap between the yarns. In such case, the typicallinear structure of a conventional display board will be lost.

If the monitor resolution permits the allocation of one or more pixelsto the width of the yarn and one or more pixels to the gap between theyarns, the linear structure of the board can be simulated well. However,the gaps between the yarn will reduce the average contrast of thesimulation. For example, where the yarn is one pixel wide and the gap istwo pixels wide then, even with a completely white yarn, the averagebrightness of the screen will only be 33%.

Thus, in accordance with alternate exemplary embodiments, multiplepixels on the display can be allocated to each point along a length ofthe yarn such that the intensity can be maintained constant over severalconsecutive pixels or image spots, or only gradually varied inintensity. As a result, the linear structure of the simulated yarndisplayed on the monitor will be apparent.

Further, to improve the average contrast and brightness of a simulationwherein the width of a single yarn is represented using plural pixels, atypical yarn structure can be clearly displayed by changing, in a firststep or time, only one of n columns or rows used to represent the yarn'swidth (e.g., from black over grey to white) and keeping the intensity ofthe remaining rows of columns black. With increasing intensity theremaining n−1 columns or rows can then be subsequently changed inintensity (e.g. from black to white). As a result, a yarn which isdepicted horizontally across a display with plural rows of pixels willhave a relatively bright center along the yarn axis, with a graduallydecreasing brightness toward what would be considered the outer edges ofthe yarn.

For example, where a yarn is represented using 6 rows of pixels, thefirst row would be of relatively low intensity brightness, the secondrow would be of higher intensity brightness, and the third and fourthrows would be of even higher intensity brightness. The fifth and sixthrows would then be of brightness intensities corresponding to the secondand first rows, respectively. The relative intensities of all rows, aswell as lower and upper intensity limits, can be adjusted by the userwhile viewing the display until a satisfactory image of the yarn isachieved. The accepted simulation of the single yarn can then be used toestablish brightness limits and relative intensities for use insubsequent simulation of a fabric.

In accordance with exemplary embodiments, increasing contrasts can alsobe used to accommodate a situation where the optical effect of thesimulation is not equally good for different settings or values of theintensity, thereby degrading visual perception of the yarn. The opticaleffect of the simulation can be degraded if, for example, the screen isset for too high of an intensity, such that the image of the simulationmay be deceiving. To address this potential degradation of the opticaleffect in accordance with an exemplary embodiment, a 100% black imagespot can be allocated to a diameter of the yarn which is below the meanvalue by an exemplary amount of 35%, while a 100% white image spot canbe allocated to a diameter exceeding the mean value by, for example,35%. Additionally, yarn portions having diameters which are below orwhich exceed the mean diameter can be optically increased not only byincreasing the intensity, but also by increasing the area covered in thepicture as described previously. For example, thin places or thickplaces which represent faults in the yarn can be artificially extendedlengthwise or widthwise over one or more rows or columns of pixels orimage spots to highlight these places in the simulated yarn.

Thus, for an area of the yarn which is below a minimum diameter (forexample, at a given location along the length of the yarn, a measuredmass obtained from the FIG. 2 graph is below a predetermined thresholdestablished relative to the mean value, such as a threshold of 35% belowthe mean value), the brightness of all pixels used to represent thatportion of the yarn can be increased and the pixels can be representedas 100% white spots. Further, the pixels immediately adjacent the pixelsused to represent that portion of the yarn, in a direction along thelength of the yarn, can be increased in brightness to highlight theexistence of a thin spot. Similarly, thick spots can be represented withan increased number of 100% white image spots.

In accordance with exemplary embodiments, display screens or videoboards having any resolution can be used. However, screens or videoboards which are only able to represent a reduced number of grey values(e.g. personal computers having so called VGA screens which only includea limited number of discrete grey values, such as 5 grey values) candegrade the quality of the simulation. Although availablegraphics-software often includes a mode which can be used to produce afixed set of intermediate grey values, the use of this mode can, forsingle image points, create its own pattern which may interfere with thepattern to be created by the simulation. Similar problems can occur withthe use of a black and white plotter or printer.

Accordingly, an improved simulation can be provided with the equipmentdescribed above if special attention is given to the foregoing effects.For example, rather than using a fixed set of intermediate color or greyvalues, interpolation between two given colors or grey values can beperformed using known interpolation techniques, to in effect increasethe number of available grey values which can be used to represent theyarn. Further, where each point along the length of yearn is representedby a block of pixels (for example, a 3×3 pixel array), a comparableeffect can be achieved by randomly distributing black spots or pixelswithin each block, the distribution being performed with a densitycorresponding to the desired degree of blackening or attenuation usingpixel patterns chosen to influence the apparent lightness or darkness ofan area on the display. For example, the simulation can be improved bydividing the portion of a display used to represent each point of asingle yarn into an area covering 5 to 20 pixels. The black spots inneighboring areas having different grey values or intensities can thenbe distributed with increased care (that is as regularly or uniformly aspossible), and to make sure that the mean number or amount of such blackspots distributed in each area corresponds exactly to the desired greyvalue in each area.

If a spectrogram as described with respect to FIG. 3 is used in thesimulation for representing the yarn rather than using the originalsignal derived from the yarn (as illustrated in FIG. 2), then unwanted“moiré-effects” can appear when calculating the grey values for eachpixel using known Fourier-Transformation formulae, such as the InverseDiscrete Fourier Transformation. To avoid these effects, the phase orfrequency of signals in the spectrogram located between chimneys can bevaried randomly within a range, such as a range corresponding to thedistance between chimneys in the spectrogram. That is, the chimneys canbe considered to define channels of the FIG. 3 spectrogram, with eachchannel being defined as a distance between two adjacent discretechimney frequencies or frequency ranges for which the spectrogram isestablished.

Thus, frequencies associated with wavelengths located between the FIG. 3chimneys can be randomly represented within the simulation with lowintensity, while frequencies associated with the chimneys can besimulated with high intensity to ensure that they are adequatelyrepresented. When varying the phase, the phase can be varied until ananalog frequency dispersion is obtained, because, as a consequence ofvarying the phase, the frequency will also vary. To obtain a clearpicture of truly periodic faults represented by the chimneys of FIG. 3,such faults can be detected using known filter-algorithms and eliminatedfrom the spectrogram. These periodic faults can then be subsequentlyadded to the calculated yarn signal by adding sinusoidal functions orwaves having an amplitude which corresponds to the chimneys.

When simulating yarn with the frequencies derived from a spectrogram, itis possible that other periodic waves are present which correspond towavelengths of the spectrogram used for display purposes, but which donot have a frequency corresponding exactly to an integer multiple of thefundamental wave. This can be due, for example, to the fact that theresolution of the spectrogram is not infinite. If harmonic waves withina certain range of an integer multiple are forcedly given a frequencywhich is an exact integer multiple of the fundamental wave, then theimage of the simulation will be improved since the intensity of theperiodic faults will be further accentuated in the display.

When woven fabrics are to be simulated, the structure and the dimensionof the fabric can have a large influence on the quality of thesimulation to an extent to which the simulated fabric corresponds to thereal fabric. The simulation can, for example, be improved by taking intoaccount the width of the fabric when simulating the gap between adjacentyarns on the display relative to yarn width.

Thus, in accordance with exemplary embodiments, a fabric to be simulatedon a display can be used to partition the display among pixels whichwill be used to represent yarn and pixels which will be used torepresent the black board. After allocating the pixels accordingly, theintensity of each pixel used to represent the yarn in the fabric can bedetermined. For example, all frequencies of the spectrogram shown inFIG. 3, other than frequencies associated with the chimneys, can be usedto allocate a given intensity to each pixel along the length of eachyarn in the display. Afterwards, the intensities of pixels affected bythe frequencies associated with the chimneys can be modified.Subsequently, pixels affected by imperfections in the yarn (e.g., neps)can be modified in intensity. As described previously, where a givenpixel is determined to be associated with an imperfection, then one ormore adjacent pixels associated with that pixel can be modified inintensity as well. For example, the total number of imperfectionsdetected along a given length of the yarn can be calculated, and thenrandomly distributed in the display. After viewing the entire display offabric, if brightness and/or contrast is inadequate, the display can bemodified to further highlight imperfections by, for example, increasingthe intensity of pixels used to represent chimneys and/or imperfections.

It will be appreciated by those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restricted. The scope of the invention is indicated by theappended claims rather than the foregoing description and all changesthat come within the meaning and range and equivalence thereof areintended to be embraced therein.

What is claimed is:
 1. A method of displaying at least one yarn qualitywhich has been measured at a plurality of locations along a length ofyarn, comprising: assigning a display attribute to each measuredquality; dividing the display attributes into a number of groups eachrepresenting a portion of the length of yarn; and displaying the displayattributes of the groups side-by-side to facilitate comparison of thequality in the groups.
 2. A system for electronically displaying atleast one yarn quality which has been measured by means for measuring ata plurality of locations along a length of yarn, comprising: means forassigning a display attribute to each measured quality; means fordividing the display attributes into a number of groups, eachrepresenting a portion of the length of yarn; and means for displayingthe display attributes of the groups side-by-side to facilitatecomparison of the quality in the groups.
 3. The system of claim 2further including a video display for displaying the display attributes.4. The system of claim 2 in which the display attribute is a linesegment.
 5. The system of claim 2 in which the display attribute iscolor.
 6. The system of claim 2 in which the display attribute is greyscale.
 7. The system of claim 2 in which said means for measuringmeasures at least two different yarn qualities.
 8. The system of claim 7in which said means for assigning includes means for providing adifferent display to attribute for each measured yarn quality.
 9. Asystem for electronically comparing yarn lengths to assist in gradingyarn quality, comprising: means for determining the yarn diameter at anumber of locations along a length of yarn; and means for displayingrepresentations of the diameters of the yarn to allow comparison of yarnportions.
 10. The system of claim 9 further including means for dividingthe diameters into a plurality of groups, each group representing aportion of the length of yarn.
 11. The system of claim 10 in which thegroups of diameters are adjacent so that the portion of yarn measured iscontinuous.
 12. The system of claim 9 in which said means for displayingincludes means for assigning different representation parameters todifferent yarn diameters.
 13. The system of claim 12 in which saidrepresentation parameters include different grey values for a monochromedisplay.
 14. The system of claim 12 in which representation parametersinclude different colors for a color display.
 15. The system of claim 9in which said means for displaying representations includes a videodisplay.
 16. The system of claim 10 in which said means for displayingrepresentations includes means for displaying the representations of thegroups side-by-side to facilitate comparison of the groups.
 17. Thesystem of claim 10 in which the groups represent yarn portions ofdifferent lengths.
 18. A system for electronically displayinginformation concerning yarn lengths to assist in judging quality,comprising: means providing a yarn measurement zone; means for movingyarn through the measurement zone; means for measuring a quantityrelated to yarn diameter at a number of closely-spaced locations along alength of yarn; means for dividing such measured quantities relating todiameters into a plurality of groups each representing a portion of thelength of yarn; means for assigning different representation parametersto different measured quantities; and means for displaying therepresentation parameters of the yarn portions side-by-side on a videodisplay to allow comparison of the yarn portions.